The present invention relates to an internal combustion engine which comprises at least one cylinder, at least two suction valves per cylinder, and individual suction channels of longer and shorter length for each cylinder, each suction channel communicating with a suction valve.
During the suction stroke of a piston engine, it is desirable for as large mass of air as possible to be delivered to the cylinder space. For this reason it is usual for each cylinder to be provided with several suction valves and suction channels. When the suction valves are opened, air flows through the suction channels and into the cylinder space. A low-pressure wave then propagates in the suction channels in the direction from the cylinder space. When the low-pressure wave reaches an open end of the respective suction channel, a high-pressure wave is formed which flows in the direction towards the cylinder space. By arranging the suction channels with different lengths, the high-pressure wave in the respective suction channel reaches the cylinder space at different times. If one or more of the suction channels are provided with a length which is adapted so that the high-pressure wave reaches the cylinder space at the end of the suction stroke or the start of the compression stroke, the quantity of air in the cylinder space can be increased.
From U.S. Pat. No. 5,009,200 it is already known to provide an internal combustion engine with a suction arrangement in which the suction channels to the respective suction valve have different lengths. At a low engine speed, only the longest suction channel is open, while the shorter ones are closed with the aid of throttles. As the engine speed increases, the throttle in one of the short suction channels is opened, at the same time as the effective length of the long suction channel is shortened by means of a side throttle belonging to this channel being opened. At high engine speeds, all the throttles of the suction channels are opened, at the same time as the effective length of the longer suction channels is shortened by means of side throttles so that the effective length of all the suction channels is identical.
A disadvantage of this suction arrangement is the large number of throttles required for the suction arrangement to function. This suction arrangement therefore requires a large number of moving components and a special control arrangement for controlling the throttles.
One object of the present invention is to make available an internal combustion engine of the type set out in the introduction, which comprises a small number of components specially intended to control the suction of air for the purpose of increasing the torque and power of the internal combustion engine.
Another object of the invention is to make available an internal combustion engine in which the components which are specially intended to control the suction of air occupy a small space.
According to the invention, this is achieved by means of at least two of the suction valves having different closing times.
In such an internal combustion engine, there is no requirement for separate throttles which open and close the suction channels. Instead, the suction valves of the internal combustion engine are used to open and close the suction channels at defined points in time. As a result of this, the suction arrangement takes up a small amount of space.